To permit measurement of catecholamines in minute regions of the mouse brain, the method of Palkovits et al., 1974 was modified by acetylating the 3H-methylated catecholamines before thin layer chromatography. Stable adducts were formed which permitted detection of E, NE, and DA at the 10 pg level. With this assay, we have found evidence for selective age-related impairment of dopamine containing neurones in the striatum, median eminence, and neural lobe of the pituitary of C57BL/6J male mice. Since similar decreases of dopamine are reported during normal aging in human brain, the inbred mouse may be seriously considered as a useful model for some neuronchemical aging changes.